Field of the Invention
The present invention relates in general to malfunction detecting systems for use in automotive automatic transmissions of a type which comprises a torque converter and a transmission gear train. More specifically, the present invention is concerned with a malfunction detecting system for a rotation-speed-measuring device which measures rotation speed of the output means (or turbine) of the torque converter of an automatic transmission.
Description of the Prior Art
In order to appropriately control automotive automatic transmissions of the above-mentioned type, various control systems have been hitherto proposed, almost all of which are designed to control the line pressure applied to hydraulically operated parts of the transmission. In fact, as is shown in "SERVICE MANUAL FOR RE4RO1A TYPE AUTOMATIC TRANSMISSION" issued from NISSAN MOTOR CO., LTD. in March, 1987, these conventional control systems are designed to control the line pressure in accordance with the opening degree of a throttle valve of the associated internal combustion engine.
In order to eliminate or at least minimize unavoidable drawbacks encountered in these conventional control systems, a measure has been proposed by, for example, Japanese Patent application No. 63-17349. In the measure of this Application, the rotation speed of the output means (or turbine) of the torque converter is measured by a so-called "turbine speed measuring device" and the rotation speed thus measured is used as one of control factors for the line pressure.
However, the measure proposed by the Application fails to provide the turbine speed measuring device with a so-called "malfunction detecting system" by which the malfunction of the turbine speed measuring device is detected. Thus, when the measuring device becomes out of order during running of the associated motor vehicle, the transmission, and thus, the motor vehicle is subject to a trouble without giving any alarm to a driver.